1. Field of the Invention
This invention relates to an apparatus for controlling a continuously variable transmission (hereinafter called CVT) used for a power transmission system of a vehicle.
2. Description of the Prior Art
A CVT is used for a vehicle as a power transmission system which is to control continuously speed ratio e (=output side rotational speed Nout/input side rotational speed Nin) to run an internal combustion engine with a satisfactory specific fuel consumption. In general vehicles with the CVT are set the output horse power and throttle position of the engine as a function of pedalling amount of an accelerator pedal, and an engine speed Nx by which each output horse power is obtained from a minimum specific fuel consumption (unit; g/Ps.h) in the corresponding throttle position or an engine speed Nx' obtained from a proper correction corresponding to parameters of vehicle speed V or the like, on the basis of the engine speed Nx (hereinafter Nx, Nx' will be called "optimum engine speed No") is set to a desired engine speed Ne'. Also, an idle switch for detecting the idling position of the throttle valve (strictly speaking, a general idle switch is not to detect only the throttle position. It is turned on when the throttle position is below a position slightly exceeding the idling position and turned off when the throttle position exceeds said position) is provided to fully cut off ("cut") fuel for restraining fuel consumption during a period of vehicle deceleration when the idle switch is turned on, while the fuel is cut only when the engine speed Ne exceeds the minimum engine speed Nl for the fuel cut condition to avoid the engine stop. When the desired engine speed Ne' is set to said optimum engine speed No during a period of vehicle deceleration, the actual engine speed Ne becomes less than the minimum engine speed Nl for the fuel cut condition for a short time. Thus, during a period of vehicle deceleration, the desired speed Ne' is set to an engine speed Nf (provided Nf&gt;Nl) for the fuel cut determined separately from the optimum engine speed No to increase the fuel cut time. In general travelling, the accelerator pedal may be often slightly pedalled for the purpose of restraining deceleration during deceleration of vehicle or the like purpose and then further pedalled to accelerate the vehicle. In a conventional CVT, when the accelerator pedal is slightly pedalled, the desired engine speed Ne' is largely reduced from the relative high engine speed Nf for fuel cut to the optimum engine speed No to degrade acceleration responsive property when the accelerator pedal is next pedalled substantially to accelerate the vehicle, while increasing the pedalling amount of the accelerator pedal for necessary acceleration and thereby disadvantageously degrading the specific fuel consumption.